As used herein, the term “display” is intended to broadly encompass any informational, pictorial or graphic displays, e.g., containing alphabetic and/or numeric text, graphic components, icons, symbols or other visually discernable indicia. These displays may be used in various contexts as signs, panels or any other visual display. One specific and non-limiting example of such a display is a fixed-image sign for emergency lighting purposes, such as an EXIT sign used to indicate an exit or egress path from a building in the context of commercial building construction. Other examples include informational displays in a variety of other locations and/or contexts different from emergency lighting, such as displays indicated “LASER IN USE,” “AREA OF RESCUE ASSISTANCE,” “MRI ON,” or “ON THE AIR.”
In the specific context of signs for emergency lighting, building codes, transportation safety codes, and/or other regulations require such signs to be plainly visible and to be illuminated at all times when a building is occupied.
Certain emergency lighting signs include internal energy/light sources powered by building/mains power. With respect to common incandescent, neon, and fluorescent light sources, such essentially continuous illumination is expensive and inefficient.
Standard photoluminescent emergency lighting signs are commonly available that do not contain an internal energy source, but require a continuous source of ambient light to provide adequate activation when building/mains power is available. This is typically provided from a lighting fixture mounted in close proximity to the photoluminescent exit sign, which in many cases requires a costly and high power consuming installation primarily required to activate the emergency lighting sign as well as periodic maintenance to ensure adequate activation.
Such ambient light-based systems are susceptible to downtime due to power failures in the electrical power grid. To provide illumination in the event of building power failure, some hybrid signs have been developed to provide multiple illumination modes. Such hybrid photoluminescent signs typically consist of a code-approved legend illuminated by an internal energy source that provides required illumination for a means of egress from an internal source when building/mains power is available, and from an afterglow from photoluminescent material that has been activated from said internal source after mains power becomes unavailable.
U.S. Pat. Nos. 6,364,498, 6,843,010 and 7,412,790 disclose exemplary signs with multiple illumination modes. For example, U.S. Pat. No. 6,364,498 discloses a sign that uses a powered light source to illuminate lettering/characters and to energize photo-luminescent pigment during normal operation. The pigment glows and thereby illuminates the lettering in the event of a power failure.
Alternatively, some signs have been developed to include battery backup systems. However, battery backup systems have several limitations and/or disadvantages, including that they consume power essentially all of the time, which is still further expensive and inefficient. In addition, batteries have limited lives, and thus require periodic testing of the sign and frequent battery replacement, which has a resulting adverse environmental impact.
To address the inefficiency of battery backup systems and/or signs with incandescent or other light sources, some energy efficient signs have been developed that use energy-efficient LEDs as the light source. U.S. Pat. Nos. 7,937,865, 8,302,336, 8,539,702, and 6,883,926 disclose exemplary signs using LEDs as a light source.
Unlike energy inefficient incandescent, neon and fluorescent light sources that produce white (broad visible spectrum) light, many energy-efficient LEDs do not generate white light. In the context of exit signs, the desired color is most often red (625 nm) or green (520 nm). Though energy-efficient, many LEDs are objectionable in that provide undesirably low radiative performance in the desired color spectrum, and/or undesirably high radiative performance outside the desired color spectrum.
What is needed is an illuminated display comprising having illumination components providing multiple modes of efficient illuminated operation, while also provide enhanced radiative performance in a selected band of the visible light spectrum, such as the red or green spectrum for emergency lighting signs.